Add pre_apt_script

This allows to perform actions before 'apt action' run.
Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>

flatdeb/debos-runtimes.yaml

@@ -4,6 +4,7 @@
 {{- $suite := or .suite "stretch" -}}
 {{- $flatpak_arch := or .flatpak_arch $architecture -}}
 {{- $packages := or .packages "" -}}
+{{- $pre_apt_script := or .pre_apt_script "" -}}
 {{- $post_script := or .post_script "" -}}
 {{- $sdk := or .sdk false -}}
 {{- $sdk_packages := or .sdk_packages "" -}}
@@ -54,6 +55,13 @@ actions:
     chroot: false
     command: 'echo; "$RECIPEDIR/prepare-runtime" "$ROOTDIR"'
 
+  {{ if $pre_apt_script }}
+  - action: run
+    label: pre_apt_script
+    chroot: true
+    script: '{{ $pre_apt_script }}'
+  {{ end }}
+
   {{ if $packages }}
   - action: run
     label: apt-install

run.py

@@ -1123,6 +1123,20 @@ class Builder:
                     argv.append('-t')
                     argv.append('post_script:post_script')
 
+                pre_apt_script = self.runtime_details.get('pre_apt_script', '')
+
+                if pre_apt_script:
+                    dest = os.path.join(scratch, 'pre_apt_script')
+
+                    with open(dest, 'w', encoding='utf-8') as writer:
+                        writer.write('#!/bin/sh\n')
+                        writer.write(pre_apt_script)
+                        writer.write('\n')
+
+                    os.chmod(dest, 0o755)
+                    argv.append('-t')
+                    argv.append('pre_apt_script:pre_apt_script')
+
                 if sdk:
                     sources_tarball = sources_prefix + '.tar.gz'